The Delta independent., 1887-01-18
LESSONS OF THE EARTHQUAKE.

North America, and particularly of the
United States. owes its present condi-
ton to an upward bending of the
earth's crust. Besides much irregular
crumpling and cracking in various d.
rections, this bend produced line Of
weakness and fracture, starting near
Troy, New York, and running about
parallel to the coast line to near
Raleigh. North Carolina, where it bends
towards the south and disappears.
After the fracture was formed, the lay
ers of limestone making the surface
| portion, moved upon one another to
some extent, but have rested quietly
with little, if any, motion for a very
long period, long enough to efface all
external marks of the crumpling in
many places through wearing away of
the surface.
Judging from the known records, we
have good reason to suppose that not
a minute passes without motion in some
part of the earths surface. Most of
these movements, all of which come
under the general name of earthquakes,
are SO small that no notice is taken of
them. and only delicate instruments
record their existence. So the earth is
practically stable.
The common opinion has been that
tho eastern part of this continent is
free from earthquakes of any marked
severity, and that its surface never
changes. The shock of August 81, felt
over wide area, extending all the way
from the Atlantic and Gulf Coast to
Canada, has shaken this opinion. 1t
was the most severe earthquake
recorded as felt in the United States.
The point of greatest destruction
was Charleston, South Carolina. and a
large part of that city was badly in
jured and some buildings completely
destroyed. The first or principal shock,
of the evening of August 81. was fol-
lowed by others in long series, each
one, however, less severe than the one
Immediately before it. Observers de-
clare that the shock came from the
southwest and passed away to the
northeast. If the press accounts of
the time are reliable, the real motion of
the eastern part of the country was in
the opposite direction. 1t was re-
markable more for the extended area
over which the motion was felt than
for its severity. 1t was especially de-
structive to Charleston, which lies near
its central point. The cause of the
movement acted there, and then a
wavelike motion of the earth followed
which was felt until it had ex-
pended its force. 1t gradually died out
according to the usual law Of vibrations,
for their intensity diminishing inverse
ly as the square of the distance, so that
at a hundred miles the shock would be
only one-fourth as severe as at fifty
miles from the disturbance. Delicate
instruments would undoubtedly have
recorded the movement at points very
much further from Charleston than the
most distant place where the shock
was perceived
The general phenomena of earth
quakes are well known. The one at
Charleston was typical. They are
simply waves in the ground in all re-
spects like waves in water, but smaller,
because the ground is harder. But the
cause of the movement is not always
known. Here there is some room for
conflicting views. In some cases, it is
certainly connected with volcanic
eruptions, and then it seems probable
that the melted lava is moving along
under the ground. But when the GEN.
tire of the shock is long distance from
any volcano, this cannot be the cause,
and many other theories have been pro-
posed to account for the effects. some
of them conflicting and even asburd.
The conditions of earthquakes are GER
tainly not all known, and until they
are, no complete theory can be formed.
Earthquakes really depend upon the
condition of the earth's interior. So
far, no way has been found to deter
mine this with certainty. If the indica-
tions shown within moderate depths
arc reliable. it must be hot enough
| "ituiu d VI lue euTlhCc
to melt all common substances, proba-
by so within thirty miles. while the
pressure is sufficient to cause ready
motion. like liquids. The hard crust
is only the part of the earth which has
already cooled down. But the earth
has not yet ceased cooling, and it will
not utill all bodies in the heavens reach
| the same temperature. The result of this
cooling is contraction; the whole earth
grows smaller, and this must cause
movements in the solid portion. Even
| if the contraction is an exceedingly
small amount, still the cause is suffi-
cient to make frequent movements
Perhaps some of these motions may at
times allow masses of confined gas to
accumulate and then escape at any
weak point with almost explosive vio-
lence.
| There is another result which must
follow the contraction of the earth,
and it certainly has followed in the
past upon a magnificent scale, as our
mountains all show it. The different
| LAYERS of the earth bncome bent and